Manganese salt additives for aluminized propellants



W 9 1956 B. c. HARBERT 3,245,850

MANGANESE SALT ADDITIVES FOR ALUMINIZED PROPELLAN'I'S Filed Oct. 26, 1950 no PERCENT ALUMINUM (22 IO PERCENT ALUMINUM (22 WITH 2 PERCENT MANGANESE CARBONATE EFFECT OF MANGANESE CARBONATE ON COMBUSTION CHARACTERISTICS OF ALUMINIZED PROPELLANTS (BURNED IN OXYGEN) INVENTOR B. C. HARBERT A TTORNEVS United States Patent 3,245,850 MANGANESE SALT ADDITIVES FOR ALUMINIZED PROPELLANTS Bobby C. Harbert, Waco, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 26, 1960, Ser. No. 65,232 14 Claims. (Cl. 14919) This invention relates to aluminized propellants. In one aspect this invention relates to increasing the utilization of aluminum in solid composite type propellant systems.

Solid prepellants can be classified with respect to composition as double base type, single base type, and composite type. An example of a double base propellant is Ballistite which comprises essentially nitroglycerine and nitrocellulose. Examples of single base propellants are nitrocellulose and trinitrotoluene. Composite type propellants are generally composed of an oxidizer, and a binder or fuel. Said composite type propellants may contain other materials to facilitate manufacture, or to increase ballistic performance such as a high energy additive. Examples of said high energy additives commonly used in composite type propellants are the finely divided metals such as aluminum, boron, magnesium, iron, beryllium, lithium, alloys of aluminum, alloys of magnesium, and mixtures thereof.

Rocket propellants have achieved considerable commercial importance as well as military importance. Jet propulsion motors of the type in which the propellants of this invention are applicable can be employed to aid a heavily loaded plane in take-off. Said motors can also be employed as an auxiliary to the conventional power plant when an extra surge of power is required. Said motors can also be employed to propel projectiles and land vehicles. Said propellants can also be used for uses other than propulsion. For example, they can be used as gas generators in starting devices, power units where a fluid is employed as a motive force, and other applications Where a comparatively large volume of gas is required in a relatively short period of time.

Strands of non-metallized ammonium perchlorate propellant when burned at atmospheric pressure produce a visible flame which extends about 1 to 2 inches from the propellant burning surface. This flame is composed primarily of hot combustion gases with entrained incandescent particles. When aluminum is used as a high energy additive in such propellants, the flame characteristics are quite different. Reaction of the aluminum is not completed in the primary reaction zone which extends only a very short distance from the burning surface of the propellant and in many instances is not complete a considerable distance downstream of the combustion zone as indicated by the visible flame. Thus, it is possible that in a rocket motor a considerable portion of the aluminum passes through the rocket motor combustion chamber unreacted. In fact, it is well known that some highly aluminized propellants deliver a smaller percentage of expected performance in engine firings than do similar conventional nonmetallized propellant systems.

I have discovered that the combustion of aluminum particles in solid composite type propellants is greatly accelerated by the inclusion of manganese salts, especially manganese carbonate and manganese sulfate, in the propellant. Thus, broadly speaking, the present invention resides in a solid composite type propellant composition comprising a major proportion of an oxidizer component, a minor proportion of a binder component, a minor proportion of finely divided aluminum as a high energy additive and a small but effective amount of a manganese salt as a combustion modifier additive.

An object of this invention is to provide an improved 'ice solid composite type propellant. Another object of this invention is to provide an additive for increasing the efliciency of combustion of solid propellants containing finely divided aluminum as a high energy additive. Another object of this invention is to provide a improved aluminized propellant composition containing ammonium perchlorate or an alkali metal perchlorate as the major portion of the oxidizer component and having incorporated therein a small but effective amount of a manganese salt for accelerating the combustion of the aluminum in said propellant. Other aspects, objects and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention there is provided a solid propellant composition comprising: a major amount of an oxidizer component selected from the group of solid inorganic oxidizing salts consisting of ammonium perchlorate, the alkali metal perchlorates, ammonium nitrate, the alkali metal nitrates, and mixtures thereof, at least a major portion of said oxidizer component being at least one of said perchlorates; a minor amount of a binder component comprised of a rubbery material; a minor amount of finely divided aluminum as a high energy additive; and a small but effective amount of a manganese salt as a combustion modifier additive.

The amount of said manganese salt utilized in the practice of the invention is usually within the range of'0.2 to 3 weight percent, preferably 0.2 to 2.0 weight percent of the total composition. The presently most preferred manganese salts are manganese carbonate and manganese sulfate. Examples of other manganese salts which can be used in the practice of the invention include, among others, manganese boride, manganese carbide, manganese chloride, manganese chromite, manganese fluoride, manganese nitrate, manganese pyrophosphate, manganese sulfide, manganese thiocyanate, and others, including mixtures of manganese salts.

The binder component of the propellant compositions of the invention can comprise any suitable flexible rubbery material. Examples of suitable flexible rubbery materials include, among others, natural rubber, synthetic rubber, or a mixture of natural rubber and a synthetic rubber. Thus, the invention is not limited to any specific rubbery material. Some examples of a suitable synthetic rubber are the rubbery polymers such as polybutadienes; polyisobutylene; polyisoprene; polyurethanes, copolymers of isobutylene and isoprene; copolymers of conjugated dienes with comonomers such as styrene, alkyl styrenes, acrylic acid, polymerizable heterocyclic nitrogen bases, and acrylic acid esters such as methyl acrylate, ethyl acrylate, and the like; and polysulfide polymers or elastomers prepared by the reaction between an aliphatic dihalide and sodium sulfide. I

Said synthetic rubbery polymers can vary in consistency from liquid polymers having a viscosity of from 40 to 2000 poises, preferably 200 to 900 poises at 77 F., through very soft rubbers, i.e., materialswhich are soft at room temperature but will show retraction when relaxed, to those having a Mooney value (ML-4 at 212 F.) up to 100. Rubbery polymers having a Mooney value in the range of S to 50 are frequently preferred. Said polymers can be prepared by any methods known to the art.

Said copolymers of conjugated dienes with polymerizable heterocycl-ic nitrogen bases comprises a presently prefferred class of rubbery polymers for use in the binder component of the propellants of the invention. A presently preferred rubbery polymer is a copolymer of 1,3- butadiene with .2-methyl-S-vinylpyridine. One convenient method for preparing these copolymers is by emulsion polymerization at temperatures in the range between 3 and 140 F. Recipes such as the iron pyrophosphatehydroperoxide, either sugar-free or containing sugar, the sulfoxylate, and the persulfate recipes are among those which are applicable. It is advantageous to polymerize to high conversion as the unreacted vinylpyridine monomer is difi icult to remove by stripping.

The conjugated dienes employed with the polymerizable 'heterocyclic nitrogen bases, and also with the other comonomers mentioned above, are those containing from 4 to 10 carbon atoms per molecule and include, 1,3-butadiene, isoprene, 2-methyl-1,3-butadiene, and the like. Various alkoxy, such as methoxy, ethoxy, and cyano derivatives of these conjugated dienes, are also applicable. Thus, other dienes, such as phenyl butadiene, 2,3-dimethyl- 1,3 hexadiene, 2-methoXy-3-ethylbutadiene, 2-ethoXy-3- ethyl-1,3-hexadiene, 2-cyano-l,3-butadiene, are also applicable. Instead of using a single conjugated diene, a mixture of conjugated dienes can be employed. Thus, a mixture of 1,3-butadiene and isoprene can be employed as the conjugated diene portion of the monomer system.

The polymerizable heterocyclic nitrogen bases which are applicable for the production of the polymeric materials by polymerizing said bases with a conjugated diene are those of the pyridine, quinoline, and isoquinoline series which are copolymerizable with a conjugated diene and contain one, and only one substituent wherein R is either hydrogen or a methyl group. That is, the substituent is either a vinyl or an alpha-methylvinyl (isopropenyl) group. Of these, the compounds of the pyridine series are of the greatest interest commercially at present. Various substituted derivatives are also applicable but the total number of carbon atoms in the groups attached to the carbon atoms of the heterocyclic nucleus should not be greater than 15 because the polymerization rate decreases somewhat with increasing size of the alkyl group. Compounds where the alkyl substituents are methyl and/ or ethyl are avail able commercially.

These heterocyclic nitrogen bases have the formula where R is selected from the group consisting of hydrogen, alkyl, vinyl, alpha-methylvinyl, alkoxy, halo, hydroxy, cyano, aryloxy, aryl, and combinations of these groups such as haloalkyl, alkylaryl, hydroxyaryl, and the like; one and only one of said groups being selected from the group consisting of vinyl and 'alpha-methylvinyl; and the total number of carbon atoms in the nuclear substituted groups being not greater than 15. Examples of such compounds are 2-vinylpyridine 2-vinyl-5-ethylpyridine 2-methyl-5-vinylpyridine 4-vinylpyridine 2,3 ,4-trimethyl-S-vinylpyridine 3,4,5 ,6-tetramethyl-Z-vinylpyridine 3-ethyl-5-vinylpyridine 2,6-diethyl-4-vinylpyridine 2-isopropyl-4-nonyl-5-vinylpy'ridine 2-methyl-5 -undecyl-3-vinylpyridine 2,4-dimethyl-5 ,6-dipentyl-3-vinylpyri dine 2-decyl-5 alpha-me thylvinyl) pyridine 2-vinyl-3-rnethyl-5-ethylpyridiue Another preferred synthetic rubber polymer which can be used in the binder component of the solid propellants of the invention are the copolymers of conjugated dienes, for example 1,3-butadiene, with acrylic acid. Said copolymers are commonly prepared by emulsion polymerization at temperatures in the order of 50 C. using various monomer ratios, commonly in the range /10 to 92/ 8 butadiene/acrylic acid. An example of a suitable recipe is Parts by weight 1,3-butadiene 92 Acrylic acid 8 Water Tertiary amine HCl salt 1 5 Sulfole 2 7 1 Such as cetyl dlmethylbenzyl ammonium chloride. Tertiary dodecyl mercaptan.

About one percent of phenyl-beta-naphthylamine is added to the polymers as an antioxidant. Said copolymers of 1,3- butadiene and acrylic acid are available commercially in viscosities ranging from 200-700 poises at 25 C. The liquid copolymers can be cured to solid synthetic rubbers using conventional curing agents such as the Epon curatives. Acids other than acrylic acid which can also be used include methacrylic acid, itaconic acid, palmitoleic acid, oleic acid, ricinoleic acid, arachidonic acid, erucic acid, selacholeic acid, fumaric acid, maleic acid, and the like.

Another synthetic rubber polymer which can be employed in the binder of the solid propellant composition of this invention is a copolymer of 1,3-butadiene with styrene. Such copolymers are commonly known in the art as GR-S rubbers. Said GR-S rubbers can be prepared by any of the well known methods employing well known recipes. Any of the well known GR-S rubbers containing from 1 to 2 and up to about 25 parts of styrene can :be used in the practice of the invention. The 6R4 rubber designated as 1 505 is one preferred copolymer for use in the practice of the invention. GR-S 1505 can be prepared by copolymerizing 1,3-butadiene with styrene at 41 F. using a sugar free, iron activated, rosinacid emulsified system. A charge weight ratio of hutadiene to styrene is 90/10 and the polymerization is allowed to go to approximately 52 percent completion. The copolymer is then salt acid coagulated and usually has a mean raw Mooney value (ML-4) of about 40. Said copolymers usually have a bound styrene content of about 8 weight percent. Further details regarding the preparation of 6R4 rubbers can be found in Industrial and Engineering Chemistry, 40, pages 769-777 (.1948) and United States Patents 2,583,277; 2,595,892; 2,609,362; 2,614,100; 2,647,109; and 2,665,269.

Another synthetic rubber material which can be enisuch as COOH, SO H, POOH, etc.

ployed in the binder component of the solid propellants of the invention are the polysulfide elastomers. Said polysulfide elastomers are well known to those skilled in the art and are commonly prepared by the condensation of an aliphatic dihalide and sodium polysulfide. The dihalide is added slowly, with vigorous agitation, to an aqueous solution of sodium polysulfide. Products ranging from viscous liquids to rubber can be obtained depending upon the amount of polysulfide and dihalide used. Excess dihalide gives viscous liquids and excess polysulfide gives solid rubbers. The reaction is exothermic, requires from 2 to 6 hours, and is best carried out at about 70 C. The rank of the polysulfide, i.e., the value of n in Na s varies in different types of the polysulfide elastomers. Dihalides which have been used com mercially are ethylene dichloride, propylene dichloride, bis(2-chloroethyl)ether, di-Z-chloroethyl formal, and 1,3- glycerol dichlorohydrin. Further details regarding said polysulfide elastomers can be found in Synthetic Rubber, G. S. Whitney, John Wiley & Sons, New York (1954) pp. 892-900.

Another preferred class of synthetic rubber materials which can be used in the binder component of the solid propellants of the invention are polymers of the above described conjugated dienes which contain functional acid groups within the polymer molecule such as polymers having the formula QY wherein Q comprises a conjugated diene polymer of the type described above, Y is an acidic group and n is at least 1 and preferably 2 to 4.

I The polymers containing terminal acidic groups can be prepared by contacting the monomer or monomers to be polymerized with between about 0.25 and about 100 millimoles per 100 grams of monomer of an organo alkali metal compound, preferably on organo polyalkali metal compound containing at least 1 and preferably from 2 to 4 alkali metal atom-s; those containing 2 alkali metal atoms are more often employed. Temperatures employed are preferably between about 75 and +75 C. The organic Said terminally reactive polymers containing an alkali metal on at least one end of the polymer chain can be treated with a stoichiometric excess of an acid forming reagent such as carbon dioxide, sulfuryl chloride, etc. at temperatures between -75 and +75 C. and hydrolyzed to provide polymers having terminal acidic groups Said polymers containing terminal acidic groups can be cured to solid .rubbery materials using tri(aziridinyl) phosphine oxides or sulfides. For example, tri(l-aziridinyl) phosphine oxide.

Further details regarding the preparation of such polymers can be found in copending application Serial No. 37,516 filed June 20, 1960 by W. B. Reynolds et al.

Still another class of synthetic rubber materials which can be used in the practice of the invention are the polyurethanes. Said polyurethanes are well known materials which are prepared by the interaction of one or more active hydrogen atom containing compounds containing at least one active hydrogen atom with a polyisocyanate. In preparing the polyurethane to form a curable fluid blend, said monomers are blended together and said fluid blend is cured to form a solid product. Said active hydrogen atom containing compound can be any suitable such compound containing at least one, but preferably at least two, reactive hydrogen atom containing groups in the molecule. Any suitable organic polyisocyanate can be used in the practice of the invention; however, diisocyanates are preferred because of their availability and ease of preparation. Both the active hydrogen atom containing compound and the diisocyanate should be liquid under the conditions of use. Said polyurethane monomers are usually reacted in substantially stoichiometric amounts (based on the active hydrogen atom functionality of the active hydrogen atom containing monomer). However, said active hydrogen atom containing monomer can be used in amounts up to about 15 weight percent in excess of stoichiometric and said polyisocyanate can be used in amounts up to about 25 weight percent in excess of stoichiometric.

Representative polyisocyanates which can be used in the practice of the invention include, among others, the following:

benzene-1,3-diisocyanate, benzene-l,4-diisocyanate, hexamethylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,5-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenyl-4,4'-diisocyanate, diphenyl-3,3'dimethyl-4,4'-diisocyanate, 2-chloropropane-1,3-diisocyanate, diphenyl-3,3'-dimethoxy-4,4'-diisocyanate, naphthalene-1,5-diisocyanate, pentamethylene diisocyanate, tetramethylene diisocyanate, octamethylene diisocyanate, dimethylene diisocyanate, propylene-1,2-diisocyanate, benzene-1,2,4-triisocyanate, toluene-2,3diisocyanate, diphenyl-Z,2'-diisocyanate, naphthalene-2,7diisocyanate, naphthalene-1,8-diisocyanate, tolenue-2,4,6-triisocyanate, benzene-1,3,5-triisocyanate, benzene-1,2,3-triisocyanate, and toluene-2,3,4-triisocyanate,

Active hydrogen atom containing compounds which can be used in the practice of the invention include those which have plasticizing properties and which are known to react with polyisocyanates to form polyurethanes. Compounds which are useful for this purpose in the practice of the invention are those which contain hydroxyl and/or amino groups, each of said amino groups containing at least one active hydrogen atom, and which are reactive with an isocyanate group, NCO. Compounds employed preferably have two or more of said reactive hydrogen atom containing groups in the molecule. Commonly, the preferred compounds are glycols and hydroxy containing esters, including polyglycols and polyesters. Polyamino compounds including diamines such as putrescine and cadaverine can also be employed. Triols such as glycerol and tetrols such as erythritol can also be used. Natural products which are particularly useful include castor oil, which comprises a glyderide of ricinoleic acid, and ricinoleyl alcohol, and mixtures thereof. Said active hydrogen atom containing compounds should be liquid under the conditions of use defined above.

Other examples of these active hydrogen atom containing compounds include alkylene glycols such as ethylene glycol, diethylene glycol, tetraethylene glycol, neopentyl glycol, compounds designated as polyethylene glycol and polypropyene gycol having a molecular weight as high as 10,000 and even higher, propylene glycol, dipropylene glycol, mixed glycols such as the ethylene-propylene glycols, butylene glycol, dibutylene glycol, pentamethylene glycol, ricinoleyl alcohol, penaerythritol [2,2-bis(hydroxymethyl)-l,3-propanediol], esters containing two or more OH groups, and the like.

In forming a polyurethane, it is sometimes desirable 7. to employ a small amount of another polyhydroxy compound as a cross-linking agent. It is preferred that said cross-linking agent have three or more hydroxy groups. Many of the above-named polyhydroxy compounds are in this preferred group of cross-linking agents. For example, representative polyhydroxy cross-linking agents include, among others, the following: saturated aliphatic and aromatic polyhydric alcohols, such as 1,2,3-propanetriol (glycerol), 1,2,6-hexanetriol, trimethylolpropane, erythritol, pentaerythritol, ribitol, xylitol, sorbitol, mannitol, trimethylolphenol, trimethylolbenzene, and the like.

The amount of said polyhydroxy cross-linking agent used in the practice of the invention will be minor, generally between 0.01 to 15 weight percent of the total propellant composition, preferably 0.25 to Weight percent. When said polyhydroxy cross-linking agents are used, the amount of polyisocyanate monomers used is based on the total active hydrogen functionality of both the polyol polymers and the polyhydroxy cross-linking agent.

Further details regarding the preparation of said polyurethanes can be found in copending application Serial No. 848,161, filed October 22, 1959 by R. C. Lippert.

The binder contains a rubbery material of the type or types hereinbefore described and, in addition, there can be present one or more reinforcing agents, plasticizers, curing agents, wetting agents, and antioxidants. Other ingredients which are employed for sulfur vulcanization include a vulcanization accelerator, a vulcanizing agent, such as sulfur, and an accelerator activator, such as zinc oxide. The finished binder usually contains various compounding ingredients. Thus, it will be understood that herein and in the claims, unless otherwise specified, the term binder is employed generically and includes various conventional compounding ingredients. The binder content of the propellant composition is a minor proportion of the total propellant composition. Commonly used amounts of binder component range from about 12 to about 20 percent by weight of the total composition although larger and smaller amounts can be used.

The copolymer comprising a conjugated diene and a polymerizable heterocyclic nitrogen base can also be cured by a quaternization reaction by incorporating therein a quaternizing agent and subjecting the resulting mixture to quaternizing conditions of temperature. Suitable quaternizing agents include alkyl halides such as methyl iodide and methyl bromide; alkylene halides such as methylene iodide and ethylene bromide; substituted alkanes such as chloroform and bromoform; alkyl sulfates such as methyl sulfate; and various substituted aromatic compounds such as benzoyl chloride, methyl benzene sulfonate, benzotrichloride, hexachloro-p-xylene, dichloro-p-xylene, benzal chloride, and the like. The quaternizing temperature is usually in the range of 0 to 175 C., although temperatures outside this range can be used.

A general formulation for the binder component of the propellant compositions of the invention is as follows:

Curing agent Reinforcing agents which can be employed include carbon black, wood flour, lignin, and various reinforcing resins such as styrene-divinylbenzene, methyl acrylatedivinylbenzene, acrylic acid-styrene-divinylbenzene, and methyl acrylate-acrylic acid-divinylbenzene resins.

In general, any suitable rubber plasticizer can be employed in the binder compositions. Materials such as Pentaryl A (amylbiphenyl), Parafiux (saturated polymerized hydrocarbon), Circosol-2XH (petroleum hydrocarbon softener having a specific gravity of 0.940 and a Saybolt Universal viscosity at F. of about 2000 seconds), di(l,4,7-trioxaundecyl) methane, ZP-21l (5,8,- l1,13,l6,19-hexosatricosane), and dioctyl phthalate are suitable plasticizers. Materials which provide a rubber having good low temperature properties are preferred. It is also frequently preferred that the plasticizers be oxygencontaining materials.

Wetting agents aid in defiocculating or dispersing the oxidizer. Aerosol OT (dioctyl ester of sodium sulfosuccinic acid), lecithin, and Duomeen C diacetate (the diacetate of trimethylenediamine substituted by a coconut oil product) are among the materials which are applicable.

Antioxidants which can be employed include Flexamine (physical mixture containing 65 percent of a complex diarylamine-ketone reaction product and 35 percent of N,N-diphenyl-p-phenylenediamine), phenyl-beta-naphthylamine, 2,2 methylene-bis(4 methyl 6 tert-butylphenol), and the like. Rubber antioxidants, in general, can be employed or if desired can be omitted.

Examples of vulcanization accelerators are those of the carbamate type, such as N,N-dimethyl-S-tert-butylsulfenyl dithiocarbamate and Butyl-Eig-ht. Butyl-Ei-ght is a rubber accelerator of the dithiocarbamate type described in Handbook of Material Trade Names by Zimmerman and Lavine, 1953 Edition, as a brown liquid; specific gravity 1.01; partially soluble in water and gasoline; and soluble in acetone, alcohol, benzol, carbon disulfide and chloroform.

It is to be understood that each of the various types of compounding ingredients can be used singly or mixtures of various ingredients performing a certain function can be employed. 'It is sometimes preferred, for example, to use mixtures of plasticizers rather than a single material.

Oxidizers which are applicable in the solid propellant compositions of the invention are ammonium perchlorate, the alkali metal perchlorates, ammonium nitrate, and the alkali metal nitnates. As used herein, the term alkali metal includes sodium, potassium, lithium, cesium and rubidium. Ammonium perchlorate is the presently preferred oxidizer. Mixtures of said oxidizers are also applicable. However, when mixtures of said oxidizers are utilized, one of said perchlonates is at least a major portion, preferably at least 75 percent by weight, of the mixture. In the preparation of the solid rocket propellant compositions, the oxidizer is ground to a particle size preferably within the range between 10 and 200 microns average particle size. The amount of oxidizer used is a major amount of the total composition and is commonly within the range of about 56 to about 86 weight percent of the total propellant composition although larger and smaller amounts can be used.

It is preferred that the finely divided aluminum high energy additive have a particle size of less than 50 microns. Said high energy additive can be used in amounts of from about 2 to about 22 weight percent of the total propellant composition. In some instances greater amounts can be used.

The various ingredients in the propellant composition can be mixed in any suitable manner. In the finished propellant the binder forms a continuous phase with the oxidizer being a discontinuous phase. When the binder component comprises a solid rubbery material, such as a solid copolymer, the dry ingredients, such as the oxidizer, can be blended into said binder on a roll mill or an internal mixer such as a Banbury or Baker-Perkins mixer can be employed. One procedure for blending the propellant ingredients utilizes a stepwise addition of the oxidizer ingredient. The binder ingredients are first mixed to form a binder mixture and the oxidizer ingredient, having the manganese salt additive of the invention and any other solid ingredients dry blended therewith, is then added to said binder mixture in increments, usually 3 to 5, but a greater or smaller number of increments can be used if desired or necessary. When the binder component comprises a material which is initially liquid and cures to a solid rubbery material, such as a liquid copolymer or a polyurethane, the oxidizer and other solid ingredients can be blended with said liquid binder material to form a uniform mixture which is cast into a mold and cured.

After the propellant composition has been formulated as indicated above, or by any other suitable mixing technique, rocket grains can be formed by casting, extrusion, or compression moulding, utilizing techniques known to those skilled in the art.

The formulated grains are usually cured before use. The curing temperature will generally be in the range between 70 and 250 F., preferably between 150 and 250 F. The curing time must be long enough to give the required creep resistance and other mechanical properties in the propellant. Said curing time will generally range from around 2 hours, when the higher curing temperatures are employed, to 7 days when the lower curing temperatures are employed.

It has been observed when conventional aluminized propellants are burned in air at atmospheric pressure that incandescent particles forming luminescent streamers are projected a considerable distance from the surface of the burning propellant. Photographs of this process and other evidence showed that these particle streamers were due to the reaction of afterburning of unburned aluminum, which had not reacted or burned in the primary propellant combustion process, with oxygen in the air. To facilitate investigation of the invention, the afterburning of aluminum was accelerated by using an oxygen environment. A simple windowed chamber was constructed which made it possible to provide a controlled environment around the burning propellant. An oxygen environment greatly accelerates said afterburning and lit was found in burning conventional aluminized propellants that the streamers terminated (aluminum completely reacted) a reasonably short distance from the propellant source. From photographs of propellants burned in an atmosphere of oxygen, average termination distances of the streamers (height of combustion zone) were deter mined. The data with this technique could be correlated with specific impulse in actual rocket motor firings.

For example, correlating the results of a number of rocket motor firings of aluminized propellants wherein the motor efiiciency was measured, with measurements of flame height or height of combustion zone obtained on burning aluminized propellants has shown that for a propellant flame height in the order of 4 inches, the actual motor efficiency is in the order of 87 percent of heoretical. When the flame height of the aluminized propellant is in the order of 1 /2 inches, the actual motor efficiency is in the order of 95 percent of the theoretical.

EXAMPLE A series of base propellants having the following compositions were prepared in conventional manner.

1 Average particle size.

To each of the base propellants, while it was still liquid, there was added a sufficient quantity of a candidate combustion modifier additive to give a final concentration of said additive in the final propellant as indicated below in Table I. Each of said propellants was then poured into a small glass cup and cured in a conventional manner.

Each of said propellants was then ignited and burned in an atmosphere of oxygen (2 inches of mercury pressure) in an enclosed combustion hood provided with transparent windows through which the combustion could be photographed with the same camera under known conditions. From the resulting photographs and the known relationship of the photographic image to the actual flame, average termination distances of the streamers (height of the combustion zone) were determined and recorded. The results of said tests are given in Table I below. The figures given for the height of the combustion zone are an average taken from photographs of three or more runs for each combustion modifier.

The attached drawing, consisting of photographs of atypical Run A and a typical Run B, forms a part of this example and vividly illustrates the marked improvement obtained when magnesium carbonate is used as a combustion modifier.

The above data show that the manganese salts are much superior to the other combustion modifiers tested. When said salts are used in accordance with the invention, the combustion zone height is markedly reduced, more of the aluminum burns within the combustion chamber of the rocket motor, and the elficiency of said motor is increased.

While certain examples have been set forth above for purposes of illustration, the invention is not limited thereto. Various other modifications will be apparent to those skilled in the art in view of this disclosure. Such modifications are within the spirit and scope of the invention.

I claim:

1. A solid propellant composition comprising: a major amount of an oxidizer component selected from the group of solid inorganic oxidizing salts consisting of ammonium perchlorate, the alkali metal perchlorates, ammonium nitrate, the alkali metal nitrates, and mixtures thereof, at least a major portion of said oxidizer component being at least one of said perchlorates; a minor amount of a binder component comprised of a rubbery material selected from the group consisting of natural rubber, synthetic rubber, and mixtures thereof; a minor amount of finely divided aluminum as a high energy additive; and from about 0.2 to about 3 weight percent of an inorganic manganese salt as a combustion modifier additive.

2. A solid propellant composition comprising: a major amount of an oxidizer component selected from the group of solid inorganic oxidizing salts consisting of ammonium perchlorate, the alkali metal perchlorates, ammonium nitrate, the alkali metal nitrates, and mixtures thereof, at least a major portion of said oxidizer component being at least one of said perchlorates; a minor amount of a binder component comprised of a rubbery material selected from the group consisting of natural rubber, synthetic rubber, and mixtures thereof; from about 2 to about 22 weight percent of finely divided aluminum as a high energy additive; and from about 0.2 to about 3 weight percent of an inorganic manganese salt as a combustion modifier additive.

3. A solid propellant composition according to claim 2 wherein the amount of said oxidizer component is within the range of about 56 to about 86 weight percent of the total propellant composition, and the amount of said binder component is within the range of about 12 to about 20 weight percent of the total propellant composition.

4. A propellant composition according to claim 2 wherein said manganese salt is manganese carbonate.

5. A propellant composition according to claim 2 wherein said manganese salt is manganese sulfate.

6. A propellant composition according to claim 2 wherein said manganese salt is manganese boride.

7. A propellant composition according to claim 2 wherein said manganese salt is manganese carbide.

8. A propellant composition according to claim wherein said manganese salt is manganese chloride.

9. A propellant composition according to claim wherein said manganese salt is manganese chromite.

10. A propellant composition according to claim wherein said manganese salt is manganese fluoride.

11. A propellant composition according to claim wherein said manganese salt is manganese nitrate.

12. A propellant composition according to claim 2 wherein said manganese salt is manganese pyrophosphate.

13. A propellant composition according to claim 2 wherein said manganese salt is manganese sulfide.

14. A propellant composition according to claim 2 wherein said manganese salt is manganese thiocyanate.

NNNN

No references cited.

REUBEN EPSTEIN, Primary Examiner.

LEON D. ROSDOL, Examiner. 

1. A SOLID PROPELLANT COMPOSITION COMPRISNG: A MAJOR AMOUNT OF AN OXIDIZER COMPONENT SELECTED FROM THE GROUP OF SOLID INORGANIC OXIDIZING SALTS CONSISTING OF AMMONIUM PERCHLORATE, THE ALKALI METAL PERCHLORATES, AMMONIUM NITRATE, THE ALKALI METAL NITRATES, AND MIXTURES THEREOF, AT LEAST A MAJOR PORTION OF SAID OXIDIZER COMPONENT BEING AT LEAST ONE OF SAID PERCHLORATES; A MINOR AMOUNT OF A BINDER COMPONENT COMPRISED OF A RUBBERY MATERIAL SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, SYNTHETIC RUBBER, AND MIXTURES THEREOF; A MINOR AMOUNT OF FINELY DIVIDED ALUMINUM AS A HIGH ENERGY ADDITIVE; AND FROM ABOUT 0.2 TO ABOUT 3 WEIGHT PERCENT OF AN INORGANIC MANGANESE SALT AS A COMBUSTION MODIFIER ADDITIVE. 